In-line deposition processes for circuit fabrication

ABSTRACT

In one embodiment, the invention is directed to aperture mask deposition techniques using aperture mask patterns formed in one or more elongated webs of flexible film. The techniques involve sequentially depositing material through mask patterns formed in the film to define layers, or portions of layers, of the circuit. A deposition substrate can also be formed from an elongated web, and the deposition substrate web can be fed through a series of deposition stations. Each deposition station may have an elongated web formed with aperture mask patterns. The elongated web of mask patterns feeds in a direction perpendicular to the deposition substrate web. In this manner, the circuit creation process can be performed in-line. Moreover, the process can be automated to reduce human error and increase throughput.

This application is a divisional of U.S. Ser. No. 10/940,448, filed Sep.14, 2004, now allowed, which is a divisional application of U.S. Ser.No. 10/076,005, filed Feb. 14, 2002, now U.S. Pat. No. 6,821,348, thedisclosure of which is herein incorporated by reference.

TECHNICAL FIELD

The invention relates to fabrication of circuits and circuit elements,and more particularly to deposition techniques using aperture masks.

BACKGROUND

Circuits include combinations of resistors, diodes, capacitors andtransistors linked together by electrical connections. Thin filmintegrated circuits include a number of layers such as metal layers,dielectric layers, and active layers typically formed by a semiconductormaterial such as silicon. Typically, thin film circuit elements and thinfilm integrated circuits are created by depositing various layers ofmaterial and then patterning the layers using photolithography in anadditive or subtractive process which can include a chemical etchingstep to define various circuit components. Additionally, aperture maskshave been used to deposit a patterned layer without an etching step orany photolithography.

SUMMARY

In general, the invention is directed to deposition techniques usingaperture mask patterns formed in one or more elongated webs of flexiblefilm. The techniques involve sequentially depositing material throughaperture mask patterns formed in the webs to define layers, or portionsof layers, of a circuit. A deposition substrate can also be formed froman elongated web, and the deposition substrate web can be fed through aseries of deposition stations. Each deposition station may have its ownelongated web formed with aperture mask patterns. In some embodiments,each elongated web of aperture mask patterns travels in a directionperpendicular to the deposition substrate web. In this manner, thecircuit fabrication process can be performed in-line. Moreover, theprocess can be automated to reduce human error and increase throughput.

In some embodiments, circuits can be created solely using aperture maskdeposition techniques, without requiring any of the etching orphotolithography steps typically used to form integrated circuitpatterns. Aperture mask deposition techniques can be particularly usefulin fabricating circuit elements for low-cost integrated circuits such asradio frequency identification (RFID) circuits or for fabricatingcircuits for electronic displays such as liquid crystal displays ororganic light emitting diode displays. In addition, the techniques canbe advantageous in the fabrication of integrated circuits incorporatingorganic semiconductors, which typically are not compatible with etchingprocesses or photolithography.

In one embodiment, the invention is directed to an aperture maskcomprising an elongated web of flexible film, and a deposition maskpattern formed in the film, wherein the deposition mask pattern definesdeposition apertures that extend through the film. The elongated web maybe greater than approximately 50 centimeters or greater thanapproximately 100 centimeters or greater than approximately 10 meters,or greater than approximately 100 meters in length. The mask can besufficiently flexible such that it can be wound into a roll withoutdamage or forming a permanent bend. Also, the aperture mask may bereusable. Aperture masks in this form can be used as part of an in-linedeposition system.

In other embodiments, the invention is directed to in-line depositionsystems and in-line deposition methods. For example, a system mayinclude a first web of flexible film and a second web of flexible film,wherein the second web of film defines a deposition mask pattern. Thesystem may also include a drive mechanism that moves at least one of thefirst and second webs relative to the other of the first and secondwebs, and a deposition unit that deposits onto the first web of filmthrough the deposition mask pattern defined by the second web of film.Various in-line deposition methods are also described.

In additional embodiments, the invention is directed to a stretchingapparatus for aligning a deposition mask pattern with a substrate in anin-line deposition system. For example, the apparatus may include afirst stretching mechanism to stretch the first web of film in adown-web direction, a cross-web direction, or both directions in orderto align the deposition mask pattern formed in the first web of filmwith a deposition substrate. The deposition substrate may also form aweb, or alternatively may be a conveyance web carrying a series ofsubstrates. The second web of film may also be stretched in the down-webdirection, cross-web direction, or both directions.

The various embodiments of the invention can provide one or moreadvantages. For example, the invention can facilitate the fabrication ofrelatively small circuit elements using aperture mask depositiontechniques. For example, the invention can facilitate fabrication ofcircuit elements having widths less than approximately 1000 microns,less than approximately 50 microns, less than approximately 20 microns,less than approximately 10 microns, or even less than approximately 5microns. In addition, the invention can reduce costs associated withcircuit fabrication. Specifically, by streamlining the circuitfabrication process such that deposition can be performed in-line,circuits may be created more quickly and with a reduced number ofhandling steps. Moreover, by reducing human error, an automated processmay produce more reliable circuits than other processes. In this manner,an in-line process can promote increased yields.

Also, because the elongated web may be formed from polymeric material,the aperture masks in the web can be created using laser ablationtechniques. Laser ablation techniques may be faster and less expensivethan other mask creation techniques. Also, inexpensive polymericmaterials can allow the elongated web of masks to be disposable. Laserablation techniques allow for the fabrication of small depositionapertures, i.e., with widths less than approximately 1000 microns, lessthan approximately 50 microns, less than approximately 20 microns, 10microns, or even 5 microns. In addition, laser ablation techniques allowfor the creation of deposition apertures separated by a small gap, i.e.,less than approximately 1000 microns, less than approximately 50microns, less than approximately 20 microns, or even less thanapproximately 10 microns. These small deposition apertures and smallgaps can facilitate the fabrication of small circuit elements.Additionally, laser ablation techniques can facilitate the fabricationof aperture mask patterns over large surface areas allowing large areacircuits or widely spaced circuit elements to be fabricated.

Another advantage is that the polymeric material that makes up the webof aperture masks may be well suited to be impregnated with magneticmaterial. In that case, the magnetic material may be used to reduce sagduring the in-line deposition process, e.g., by application ofattractive or repulsive magnetic force. Furthermore, polymeric materialis often stretchable, which allows the mask to be stretched in order tobetter align the mask with the deposition substrate and possibly tocontrol sag. Stretching techniques in the down-web direction, thecross-web direction, or both may be used to achieve quick and precisealignment of the elongated web of aperture masks relative to theelongated web of deposition substrate material.

Details of these and other embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will become apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an aperture mask in the form of anaperture mask web wound into a roll.

FIG. 2 a is a top view of an aperture mask according to an embodiment ofthe invention.

FIG. 2 b is an enlarged view of a portion of the aperture mask in FIG. 2a.

FIGS. 3-5 are top views of aperture masks according to embodiments ofthe invention.

FIG. 6 is a block diagram of a laser ablation system that can be used toablate aperture mask webs in accordance with the invention.

FIG. 7 is a cross-sectional side view of a web of polymeric film formedwith a material on a first side.

FIGS. 8 and 9 are simplified illustrations of in-line aperture maskdeposition techniques.

FIGS. 10 and 11 are block diagrams of deposition stations according tothe invention.

FIG. 12 a is a perspective view of one exemplary stretching apparatusaccording to an embodiment of the invention.

FIG. 12 b is an enlarged view of a stretching mechanism.

FIGS. 13-15 are top views of exemplary stretching apparatuses accordingto embodiments of the invention.

FIG. 16 is a block diagram of an exemplary in-line deposition systemaccording to an embodiment of the invention.

FIGS. 17 and 18 are cross-sectional views of exemplary thin filmtransistors that can be created according to the invention.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of an aperture mask 10A. As shown, aperturemask 10A includes an elongated web of flexible film 11A, and adeposition mask pattern 12A formed in the film. The deposition maskpattern 12A defines deposition apertures (not labeled in FIG. 1) thatextend through the film. Typically, aperture mask 10A is formed with anumber of deposition mask patterns, although the invention is notnecessarily limited in that respect. In that case, each deposition maskpattern may be substantially the same, or alternatively, two or moredifferent mask patterns may be formed in flexible film 11A.

As shown, flexible film 11A may be sufficiently flexible such that itcan be wound to form a roll 15A without damage. The ability to windflexible film 11A onto a roll provides a distinct advantage in that theroll of film 15A has a substantially compact size for storage, shippingand use in an inline deposition station. Also, flexible film 11A may bestretchable such that it can be stretched to achieve precise alignment.For example, the flexible film may be stretchable in a cross-webdirection, a down-web direction, or both. In exemplary embodiments,flexible film 11A may comprise a polymeric film. The polymeric film maybe comprised of one or more of a wide variety of polymers includingpolyimide, polyester, polystyrene, polymethyl methacrylate,polycarbonate, or other polymers. Polyimide is a particularly usefulpolymer for flexible film 11A.

Aperture mask 10A is subject to a wide variety of shapes and sizes. Forexample, in exemplary embodiments, a web of flexible film 11A is atleast approximately 50 centimeters in length or 100 centimeters inlength, and in many cases, may be at least approximately 10 meters, oreven 100 meters in length. Also, the web of flexible film 11A may be atleast approximately 3 cm in width, and less than approximately 200microns in thickness, less than approximately 30 microns, or even lessthan approximately 10 microns in thickness.

FIG. 2 a is a top view of a portion of an aperture mask 10B according tothe invention. In exemplary embodiments, aperture mask 10B as shown inFIG. 2 a is formed from a polymer material. However, other flexiblenon-polymeric materials may also be used. The use of polymeric materialsfor aperture mask 10B can provide advantages over other materials,including ease of fabrication of aperture mask 10B, reduced cost ofaperture mask 10B, and other advantages. As compared to thin metalaperture masks, polymer aperture masks are much less prone to damage dueto accidental formation of creases and permanent bends. Furthermore,some polymer masks can be cleaned with acids.

As shown in FIGS. 2 a and 2 b, aperture mask 10B is formed with apattern 12B that defines a number of deposition apertures 14 (onlydeposition apertures 14A-14E are labeled). The arrangement and shapes ofdeposition apertures 14A-14E in FIG. 2 b are simplified for purposes ofillustration, and are subject to wide variation according to theapplication and circuit layout envisioned by the user. Pattern 12Bdefines at least a portion of a circuit layer and may generally take anyof a number of different forms. In other words, deposition apertures 14can form any pattern, depending upon the desired circuit elements orcircuit layer to be created in the deposition process using aperturemask 10B. For example, although pattern 12B is illustrated as includinga number of similar sub-patterns (sub-patterns 16A-16C are labeled), theinvention is not limited in that respect.

Aperture mask 10B can be used in a deposition process, such as a vapordeposition process in which material is deposited onto a depositionsubstrate through deposition apertures 14 to define at least a portionof a circuit. Advantageously, aperture mask 10B enables deposition of adesired material and, simultaneously, formation of the material in adesired pattern. Accordingly, there is no need for a separate patterningstep following or preceding deposition. Aperture mask 10B may be used tocreate a wide variety of integrated circuits, such as integratedcircuits which include a complimentary (both n-channel and p-channel)transistor element. In addition, organic (e.g., pentacene) or inorganic(e.g., amorphous silicon) semiconductor materials may be used to createintegrated circuits according to the invention. For some circuits, bothorganic and inorganic semiconductors may be used.

Aperture mask 10B can be particularly useful in creating circuits forelectronic displays such as liquid crystal displays or organic lightemitting displays, low-cost integrated circuits such as RFID circuits,or any circuit that implements thin film transistors. Moreover, circuitsthat make use of organic semiconductors can benefit from various aspectsof the invention as described in greater detail below. In addition,because aperture mask 10B can be formed out of a flexible web ofpolymeric material, it can be used in an in-line process as described ingreater detail below.

One or more deposition apertures 14 can be formed to have widths lessthan approximately 1000 microns, less than approximately 50 microns,less than approximately 20 microns, less than approximately 10 microns,or even less than approximately 5 microns. By forming depositionapertures 14 to have widths in these ranges, the sizes of the circuitelements may be reduced. Moreover, a distance (gap) between twodeposition apertures (such as for example the distance betweendeposition aperture 14C and 14D) may be less than approximately 1000microns, less than approximately 50 microns, less than approximately 20microns or less than approximately 10 microns, to reduce the size ofvarious circuit elements.

Laser ablation techniques can be used to define pattern 12B ofdeposition apertures 14. Accordingly, formation of aperture mask 10Bfrom a web of polymeric film can allow the use of fabrication processesthat can be less expensive, less complicated, and/or more precise thanthose generally required for other aperture masks such as silicon masksor metallic masks. Moreover, because laser ablation techniques can beused to create pattern 12B, the width of pattern 12B can be made muchlarger than conventional patterns. For example, laser ablationtechniques can facilitate the creation of pattern 12B such that a widthof pattern 12B is greater than approximately a centimeter, greater thanapproximately 25 centimeters, greater than approximately 100centimeters, or even greater than approximately 500 centimeters. Theselarge masks can then be used in a deposition process to create circuitelements that are distributed over a large surface area and separated bylarge distances. Moreover, by forming the mask on a large polymeric web,the creation of large integrated circuits can be done in an in-lineprocess.

FIGS. 3 and 4 are top views of aperture masks 10C and 10D that includedeposition apertures separated by relatively large widths. Still,aperture masks 10C and 10D are formed out of a web of film to allow thedeposition processes to be conducted in-line. FIG. 3 illustratesaperture mask 10C, which includes a pattern 12C of deposition apertures.Pattern 12C may define at least one dimension that is greater thanapproximately a centimeter, greater than approximately 25 centimeters,greater than approximately 100 centimeters, or even greater thanapproximately 500 centimeters. In other words, the distance X may bewithin those ranges. In this manner, circuit elements separated bylarger than conventional distances can be created using a depositionprocess. This feature may be advantageous, for example, in thefabrication of large area flat panel displays or detectors.

For some circuit layers, complex patterns may not be required. Forexample, aperture mask 10D of FIG. 4 includes at least two depositionapertures 36A and 36B. In that case, the two deposition apertures 36Aand 36B can be separated by a distance X that is greater thanapproximately a centimeter, 25 centimeters, 100 centimeters, or evengreater than approximately 500 centimeters. Again, laser ablationtechniques can facilitate the relatively large distance X because laserablation systems can be easily designed to facilitate the large areas.Moreover, laser ablation techniques can facilitate the creation ofdeposition apertures 36A and 36B to widths less than approximately 1000microns, less than approximately 50 microns, less than 20 microns, lessthan 10 microns, or even less than 5 microns. In that case, thedeposition process would not necessarily require the aperture mask to beregistered or aligned to a tolerance as small as the aperture widths.Still, the ability to deposit and pattern a circuit layer in a singledeposition process with elements separated by these large distances canbe highly advantageous for creating circuits that require largeseparation between two or more elements. Circuits for controlling orforming pixels of large electronic displays are one example.

FIG. 5 is a top view of aperture mask 10E. As shown, aperture mask 10Eis formed in a web of flexible material 1E, such as a polymericmaterial. Aperture mask 10E defines a number of patterns 12E₁-12E₃. Insome cases, the different patterns 12E may define different layers of acircuit, and in other cases, the different patterns 12E define differentportions of the same circuit layer. In some cases, stitching techniquescan be used in which first and second patterns 12E₁ and 12E₂ definedifferent portions of the same circuit feature. In other words, two ormore patterns may be used for separate depositions to define a singlecircuit feature. Stitching techniques can be used, for example, to avoidrelatively long deposition apertures, closed curves, or any aperturepattern that would cause a portion of the aperture mask to be poorlysupported, or not supported at all. In a first deposition, one maskpattern forms part of a feature, and in a second deposition, anothermask pattern forms the remainder of the feature.

In still other cases, the different patterns 12E may be substantiallythe same. In that case, each of the different patterns 12E may be usedto create substantially similar deposition layers for differentcircuits. For example, in an in-line web process, a web of depositionsubstrates may pass perpendicular to aperture mask 10E. After eachdeposition, the web of deposition substrates may move in-line for thenext deposition. Thus, pattern 12E₁ can be used to deposit a layer onthe web of deposition substrates, and then 12E₂ can be used in a similardeposition process further down the web of deposition substrates. Eachportion of aperture mask 10E containing a pattern may also be reused ona different portion of the deposition substrate or on one or moredifferent deposition substrates. More details of an in-line depositionsystem are described below.

FIG. 6 is a block diagram of a laser ablation system that can be used toablate aperture masks in accordance with the invention. Laser ablationtechniques are advantageous because they can achieve relatively smalldeposition apertures and can also define patterns on a single aperturemask that are much larger than conventional patterns. In addition, laserablation techniques may facilitate the creation of aperture masks atsignificantly lower cost than other conventional techniques commonlyused to create metal or silicon aperture masks.

As illustrated in FIG. 6, laser ablation system 60 may be a projectionlaser ablation system utilizing a patterned ablation mask, although ashadow mask ablation system or phase mask ablation system could also beused. Projection imaging laser ablation is a technique for producingvery small parts or very small structures on a surface of an objectbeing ablated, the structures having sizes on the order of between onemicron to several millimeters. In that case, light is passed through apatterned ablation mask and the pattern is imaged onto the object beingablated. Material is removed from the ablation substrate in the areasthat receive radiation. Although the system is described using anultraviolet (UV) laser, the illumination provided by the laser can beany kind of radiation having energy sufficient for ablation, such asinfrared or visible light. Moreover, the invention can, in principle, beapplied using radiation from sources other than lasers.

Laser 61 may be a KrF excimer laser emitting a beam with a shortwavelength of light of approximately 248 nm. However, any type ofexcimer laser may be used, such as F₂, ArF, KrCl, or XeCl type excimerlasers. An excimer laser is particularly useful in creating smalldeposition apertures because an excimer laser can resolve smallerfeatures and cause less collateral damage than lasers such as CO₂lasers, which emit beams with a wavelength of approximately 10,600 nm.Also, excimer lasers can be used with most polymers that are transparentto light from lasers typically used for processing metals, such asNeodymium doped Yttrium Aluminum Garnet (Nd:YAG) lasers. Excimer lasersare also advantageous because at UV wavelengths, most materials, such aspolymers, have high absorption. Therefore, more energy is concentratedin a shallower depth and the excimer laser provides cleaner cutting.Excimer lasers are pulsed lasers, the pulses ranging from 5-300nanoseconds. Laser 61 may also be a tripled or quadrupled Nd:YAG laser,or any laser having pulses in the femtosecond range.

Ablation mask 63 may be a patterned mask having pattern 62 manufacturedusing standard semiconductor lithography mask techniques. The patternedportions of ablation mask 63 are opaque to UV light, while a supportsubstrate of ablation mask are transparent to UV light. In oneembodiment, the patterned portions comprise aluminum while the supportsubstrate for ablation mask 63 is fused silica (SiO₂). Fused silica is auseful support material because it is one of the few materials that istransparent to mid and far UV wavelengths. Aluminum is useful as apatterning material because it reflects mid-UV light. A patterneddielectric stack is one alternative to aluminum.

Imaging lens 64 may be a single lens or an entire optical systemconsisting of a number of lenses and other optical components. Imaginglens 64 projects an image of the ablation mask, more specifically, animage of the pattern of light passing through the ablation mask ontosurface of object to be ablated 65. The object to be ablated is a web ofpolymeric film 66, possibly including a material 67 formed on the backside. Some suitable polymers include polyimide, polyester, polystyrene,polymethylmethacrylate and polycarbonate. The material 67 formed on theback side of the polymeric film 66 may be formed over the entirepolymeric film, or alternatively formed only in the local area of thefilm being ablated.

FIG. 7 illustrates useful structures that can form the object 65 to beablated. Specifically, FIG. 7 illustrates an object 65 to be ablatedthat includes a web of polymer film 66 with a material 67 formed on theback side, i.e. a side opposite the side incident to the laser in system60. Again, material 67 may be formed over the entire polymeric film, oralternatively formed only in the local area of the film being ablated.Material 67 provides an etch stop for the ablation process which canavoid air entrapment under the web of polymer film 66. For example,material 67 may comprise a metal such as copper.

After the ablation is complete, material 67 can be etched from the webof polymer film 66, to form an aperture mask web. Alternatively, in someembodiments, material 67, may be peeled away. Objects 65 may be createdby forming a copper layer on a web of polymer film, or by forming theweb of polymer film on a copper layer. In some cases, objects 65 maysimply be purchased in a preformed configuration. If formed, the copperlayer may be formed over the full web of polymeric film, or simply overthe portion of the web being ablated. In the later case, the copperlayer may be formed over different portions of the web for subsequentablation processes to ultimately define a web of polymeric film formedwith a number of deposition patterns.

Referring again to FIG. 6, table 69 supports and positions the object tobe ablated 65. For example, object to be ablated 65 can be fixed intoposition on table 69, such as by vacuum chuck 68, static electricity,mechanical fasteners or a weight. Table 69 can position the object to beablated 65 by moving the object 65 on the x, y and z axes as well asrotationally, such as along the z axis. Table 69 can move object 65 insteps down to approximately 5 nm, and more typically, approximately 100nm, reproducible to an accuracy of approximately 500 nm. Computercontrol of table 69 can allow preprogramming of the movement of table 69as well as possible synchronization of table movement with the emissionof light from laser 61. The table may also be manually controlled, suchas with a joystick connected to a computer.

In creating aperture masks for integrated circuit fabrication, it can beadvantageous to control the wall angle of the ablated depositionapertures so that the deposition apertures are suitable for material tobe deposited through them. Accordingly, the invention may control theablation so as to achieve an acceptable wall angle. A straight wallangle, i.e., a zero (0) degree wall angle, corresponds to a depositionaperture having walls that are perpendicular to the surface of the webof polymer film. In some cases, even a negative wall angle can beachieved, wherein the hole assumes a larger and larger diameter as thelaser ablates through the web of polymer film.

In general, the aperture wall angle should be near zero to allow theclosest possible spacing between apertures. However, if a large aperturemask is used in a deposition process with a small source, e.g., electronbeam evaporation, a wall angle greater than zero is desirable tominimize parallax in regions of the mask where the deposition fluximpinges the deposition substrate at an angle substantially differentfrom perpendicular.

A number of factors can affect the wall angle. Accordingly these factorscan be controlled to achieve an acceptable, or a desired wall angle. Forexample, the power density of the laser radiation at the substrate andthe numerical aperture of the imaging system can be controlled toachieve an acceptable wall angle. Additional factors that may becontrolled include the pulse length of the laser, and the ablationthreshold of the object or material being ablated.

FIGS. 8 and 9 are simplified illustrations of in-line aperture maskdeposition techniques. In FIG. 8, a web of polymeric film 10F formedwith deposition mask patterns 96 and 93 travels past a depositionsubstrate 98. A first pattern 93 in the web of polymeric film 10F can bealigned with deposition substrate 98, and a deposition process can beperformed to deposit material on deposition substrate 98 according tothe first pattern 93. Then, the web of polymeric film 10F can be moved(as indicated by arrow 95) such that the a second pattern 96 aligns withthe deposition substrate 98, and a second deposition process can beperformed. The process can be repeated for any number of patterns formedin the web of polymeric film 10F. The deposition mask pattern ofpolymeric film 10F can be reused by repeating the above steps on adifferent deposition substrate or a different portion of the samesubstrate.

FIG. 9 illustrates another in-line aperture mask deposition technique.In the example of FIG. 9, the deposition substrate 101 may comprise aweb. In other words, both the aperture mask 10G and the depositionsubstrate 101 may comprise webs, possibly made from polymeric material.Alternatively, deposition substrate web 10I may comprise a conveyanceweb carrying a series of discrete substrates. A first pattern 105 in theaperture mask web 10G can be aligned with deposition substrate web 101for a first deposition process. Then, either or both the aperture maskweb 10G and the deposition substrate web 101 can be moved (as indicatedby arrows 102 and 103) such that a second pattern 107 in aperture maskweb 10G is aligned with the deposition substrate web 101 and a seconddeposition process performed. If each of the aperture mask patterns inthe aperture mask web 10G are substantially the same, the techniqueillustrated in FIG. 9 can be used to deposit similar deposition layersin a number of sequential locations along the deposition substrate web101.

FIG. 10 is a simplified block diagram of a deposition station that canuse an aperture mask web in a deposition process according to theinvention. In particular, deposition station 110 can be constructed toperform a vapor deposition process in which material is vaporized anddeposited on a deposition substrate through an aperture mask. Thedeposited material may be any material including semiconductor material,dielectric material, or conductive material used to form a variety ofelements within an integrated circuit. For example, organic or inorganicmaterials may be deposited. In some cases, both organic and inorganicmaterials can be deposited to create a circuit. In another example,amorphous silicon may be deposited. Deposition of amorphous silicontypically requires high temperatures greater than approximately 200degrees Celsius. Some embodiments of polymeric webs described herein canwithstand these high temperatures, thus allowing amorphous silicon to bedeposited and patterned to create integrated circuits or integratedcircuit elements. In another example, pentacene can be deposited.

A flexible web 10H formed with aperture mask patterns passes throughdeposition station 110 such that the mask can be placed in proximitywith a deposition substrate 112. Deposition substrate 112 may compriseany of a variety of materials depending on the desired circuit to becreated. For example, deposition substrate 112 may comprise a flexiblematerial, such as a flexible polymer, e.g., polyimide or polyester,possibly forming a web. Additionally, if the desired circuit is acircuit of transistors for an electronic display such as a liquidcrystal display, deposition substrate 112 may comprise the backplane ofthe electronic display. Any deposition substrates such as glasssubstrates, silicon substrates, rigid plastic substrates, metal foilscoated with an insulating layer, or the like, could also be used. In anycase, the deposition substrate may or may not include previously formedfeatures.

Deposition station 110 is typically a vacuum chamber. After a pattern inaperture mask web 10H is secured in proximity to deposition substrate112, material 116 is vaporized by deposition unit 114. For example,deposition unit 114 may include a boat of material that is heated tovaporize the material. The vaporized material 116 deposits on depositionsubstrate 112 through the deposition apertures of aperture mask web 10Hto define at least a portion of a circuit layer on deposition substrate112. Upon deposition, material 116 forms a deposition pattern defined bythe pattern in aperture mask web 10H. Aperture mask web 10H may includeapertures and gaps that are sufficiently small to facilitate thecreation of small circuit elements using the deposition process asdescribed above. Additionally, the pattern of deposition apertures inaperture mask web 10H may have a large dimension as mentioned above.Other suitable deposition techniques include e-beam evaporation, variousforms of sputtering, and pulsed laser deposition.

However, when patterns in the aperture mask web 10H are madesufficiently large, for example, to include a pattern that has largedimensions, a sag problem may arise. In particular, when aperture maskweb 10H is placed in proximity to deposition substrate 112, aperturemask web 10H may sag as a result of gravitational pull. This problem ismost apparent when the aperture mask 10H is positioned underneathdeposition substrate as shown in FIG. 10. Moreover, the sag problemcompounds as the dimensions of aperture mask web 10H are made larger andlarger.

The invention may implement one of a variety of techniques to addressthe sag problem or otherwise control sag in aperture masks during adeposition process. For example, the web of aperture masks may define afirst side that can removably adhere to a surface of a depositionsubstrate to facilitate intimate contact between the aperture mask andthe deposition substrate during the deposition process. In this manner,sag can be controlled or avoided. In particular, a first side offlexible aperture mask 10H may include a pressure sensitive adhesive. Inthat case, the first side can removably adhere to deposition substrate112 via the pressure sensitive adhesive, and can then be removed afterthe deposition process, or be removed and repositioned as desired.

Another way to control sag is to use magnetic force. For example,referring again to FIG. 1, aperture mask 10A may comprise both a polymerand magnetic material. The magnetic material may be coated or laminatedon the polymer, or can be impregnated into the polymer. For example,magnetic particles may be dispersed within a polymeric material used toform aperture mask 10A. When a magnetic force is used, a magnetic fieldcan be applied within a deposition station to attract or repel themagnetic material in a manner that controls sag in aperture mask 10A.

For example, as illustrated in FIG. 11, a deposition station 120 mayinclude magnetic structure 122. Aperture mask 10I may be an aperturemask web that includes a magnetic material. Magnetic structure 122 mayattract aperture mask web 10I so as to reduce, eliminate, or otherwisecontrol sag in aperture mask web 10I. Alternatively, magnetic structure122 may be positioned such that sag is controlled by repelling themagnetic material within aperture mask web 10I. In that case, magneticstructure 122 would be positioned on the side of aperture mask 10Iopposite deposition substrate 112. For example, magnetic structure 122can be realized by an array of permanent magnets or electromagnets.

Another way to control sag is the use of electrostatics. In that case,aperture mask 10A may comprise a web of polymeric film that iselectrostatically coated. Although magnetic structure 122 (FIG. 11) maynot be necessary if an electrostatic coating is used to control sag, itmay be helpful in some cases where electrostatics are used. A charge maybe applied to the aperture mask web, the deposition substrate web, orboth to promote electrostatic attraction in a manner that promotes a sagreduction.

Still another way to control sag is to stretch the aperture mask. Inthat case, a stretching mechanism can be implemented to stretch theaperture mask by an amount sufficient to reduce, eliminate, or otherwisecontrol sag. As the mask is stretched tightly, sag is reduced. In thatcase, the aperture mask may need to have an acceptable coefficient ofelasticity. As described in greater detail below, stretching in across-web direction, a down-web direction, or both can be used to reducesag and to align the aperture mask. In order to allow ease of alignmentusing stretching, the aperture mask can allow elastic stretching withoutdamage. The amount of stretching in one or more directions may begreater than 0.1 percent, or even greater than 1 percent. Additionally,if the deposition substrate is a web of material, it too can bestretched for sag reduction and/or alignment purposes. Also, theaperture mask web, the deposition substrate web, or both may includedistortion minimizing features, such as perforations, reduced thicknessareas, slits, or similar features, which facilitate more uniformstretching. The slits can be added near the edges of the patternedregions of the webs and may provide better control of alignment and moreuniform stretching when the webs are stretched. The slits may be formedto extend in directions parallel to the directions that the webs arestretched.

FIG. 12 a is a perspective view of an exemplary stretching apparatus forstretching aperture mask webs in accordance with the invention.Stretching can be performed in a down-web direction, a cross-webdirection, or both the cross and down-web directions. Stretching unit130 may include a relatively large deposition hole 132. An aperture maskcan cover deposition hole 132 and a deposition substrate can be placedin proximity with the aperture mask. Material can be vaporized upthrough deposition hole 132, and deposited on the deposition substrateaccording to the pattern defined in the aperture mask.

Stretching apparatus 130 may include a number of stretching mechanisms135A, 135B, 135C and 135D. Each stretching mechanism 135 may protrude upthrough a stretching mechanism hole 139 shown in FIG. 12 b. In onespecific example, each stretching mechanism 135 includes a top clampportion 136 and a bottom clamp portion 137 that can clamp together uponan aperture mask. The aperture mask can then be stretched by movingstretching mechanisms 135 away from one another as they clamp theaperture mask. The movement of the stretching mechanisms can definewhether the aperture mask is stretched in a down-web direction, across-web direction, or both. Stretching mechanisms 135 may move alongone or more axes.

Stretching mechanisms 135 are illustrated as protruding from the top ofstretching apparatus 130, but could alternatively protrude from thebottom of stretching apparatus 130. Particularly, if stretchingapparatus 130 is used to control sag in an aperture mask, the stretchingmechanisms would typically protrude from the bottom of stretchingapparatus 130. Alternative methods of stretching the aperture mask couldalso be used either to control sag in the aperture mask or to properlyalign the aperture mask for the deposition process. A similar stretchingmechanism could also be used to stretch a deposition substrate web.

FIGS. 13 and 14 are top views of stretching apparatuses illustrating thestretching of aperture masks in a down-web direction (FIG. 13) and across-web direction (FIG. 14). As illustrated in FIG. 13, stretchingmechanisms 135 clamp upon aperture mask web 10J, and then move in adirection indicated by the arrows to stretch aperture mask web 10J in adown-web direction. Any number of stretching mechanisms 135 may be used.In FIG. 14, stretching mechanisms 135 stretch aperture mask web 10K in across-web direction as indicated by the arrows. Additionally, stretchingin both a cross-web direction and a down-web direction can beimplemented. Indeed, stretching along any of one or more defined axescan be implemented.

FIG. 15 is a top view of a stretching apparatus 160 that can be used tostretch both an aperture mask web 10L and a deposition substrate web162. In particular, stretching apparatus 160 includes a first set ofstretching mechanisms 165A-165D that clamp upon aperture mask web 10L tostretch aperture mask web 10L. Also, stretching apparatus 160 includes asecond set of stretching mechanisms (167A-167D) that clamp upondeposition substrate web 162 to stretch deposition substrate web 162.The stretching can reduce sag in the webs 10L and 162, and can also beused to achieve precise alignment of aperture mask web 10L anddeposition substrate web 162. Although the arrows illustrate stretchingin a down-web direction, stretching in a cross-web direction or both adown-web and a cross-web direction may also be implemented according tothe invention.

FIG. 16 is a block diagram of an in-line deposition system 170 accordingto an embodiment of the invention. As shown, in-line deposition system170 includes a number of deposition stations 171A-171B (hereafterdeposition stations 171). Deposition stations 171 deposit material on adeposition substrate web at substantially the same time. Then, after adeposition, the deposition substrate 172 moves such that subsequentdepositions can be performed. Each deposition station also has anaperture mask web that feeds in a direction such that it crosses thedeposition substrate. Typically, the aperture mask web feeds in adirection perpendicular to the direction of travel of the depositionsubstrate. For example, aperture mask web 10M may be used by depositionstation 171A, and aperture mask web 10N may be used by depositionstation 171B. Each aperture mask web 10 may include one or more of thefeatures outlined above. Although illustrated as including twodeposition stations, any number of deposition stations can beimplemented in an in-line system according to the invention. Multipledeposition substrates may also pass through one or more of thedeposition stations.

Deposition system 170 may include drive mechanisms 174 and 176 to movethe aperture mask webs 10 and the deposition substrate 172,respectively. For example, each drive mechanism 174, 176 may implementone or more magnetic clutch mechanisms to drive the webs and provide adesired amount of tension. Control unit 175 can be coupled to drivemechanisms 174 and 176 to control the movement of the webs in depositionsystem 170. The system may also include one or more temperature controlunits to control temperature within the system. For example, atemperature control unit can be used to control the temperature of thedeposition substrate within one or more of the deposition stations. Thetemperature control may ensure that the temperature of the depositionsubstrate does not exceed 250 degrees Celsius, or does not exceed 125degrees Celsius.

Additionally, control unit 175 may be coupled to the differentdeposition stations 171 to control alignment of the aperture mask webs10 and the deposition substrate web 172. In that case, optical sensorsand/or motorized micrometers may be implemented with stretchingapparatuses in deposition stations 171 to sense and control alignmentduring the deposition processes. In this manner, the system can becompletely automated to reduce human error and increase throughput.After all of the desired layers have been deposited on depositionsubstrate web 172, the deposition substrate web 172 can be cut orotherwise separated into a number of circuits. The system can beparticularly useful in creating low cost integrated circuits such asradio frequency identification (RFID) circuits.

FIGS. 17 and 18 are cross-sectional views of exemplary thin filmtransistors that can be created according to the invention. Inaccordance with the invention, thin film transistors 180 and 190 can becreated without using photolithography in an additive or subtractiveprocess. Instead, thin film transistors 180 and 190 can be createdsolely using aperture mask deposition techniques as described herein.Alternatively, one or more bottom layers may be photolithographicallypatterned in an additive or subtractive process, with at least two ofthe top most layers being formed by the aperture mask depositiontechniques described herein. Importantly, the aperture mask depositiontechniques achieve sufficiently small circuit features in the thin filmtransistors. Advantageously, if an organic semiconductor is used, theinvention can facilitate the creation of thin film transistors in whichthe organic semiconductor is not the top-most layer of the circuit.Rather, in the absence of photolithography, electrode patterns may beformed over the organic semiconductor material. This advantage ofaperture mask 10 can be exploited while at the same time achievingacceptable sizes of the circuit elements, and in some cases, improveddevice performance.

An additional advantage of this invention is that an aperture mask maybe used to deposit a patterned active layer which may enhance deviceperformance, particularly in cases where the active layer comprises anorganic semiconductor, for which conventional patterning processes areincompatible. In general, the semiconductor may be amorphous (e.g.,amorphous silicon) or polycrystalline (e.g., pentacene).

Thin film transistors are commonly implemented in a variety of differentcircuits, including, for example, RFID circuits and other low costcircuits. In addition, thin film transistors can be used as controlelements for liquid crystal display pixels, or other flat panel displaypixels such as organic light emitting diodes. Many other applicationsfor thin film transistors also exist.

As shown in FIG. 17, thin film transistor 180 is formed on a depositionsubstrate 181. Thin film transistor 180 represents one embodiment of atransistor in which all of the layers are deposited using an aperturemask and none of the layers are formed using etching or lithographytechniques. The aperture mask deposition techniques described herein canenable the creation of thin film transistor 180 in which a distancebetween the electrodes is less than approximately 1000 microns, lessthan approximately 50 microns, less than approximately 20 microns, oreven less than approximately 10 microns, while at the same time avoidingconventional etching or photolithographic processes.

In particular, thin film transistor 180 includes a first depositedconductive layer 182 formed over deposition substrate 181. A depositeddielectric layer 183 is formed over first conductive layer 182. A seconddeposited conductive layer 184 defining source electrode 185 and drainelectrode 186 is formed over deposited dielectric layer 183. A depositedactive layer 187, such as a deposited semiconductor layer, or adeposited organic semiconductor layer is formed over second depositedconductive layer 184. Aperture mask deposition techniques using anin-line deposition system, represent one exemplary method of creatingthin film transistor 180. In that case, each layer of thin filmtransistor 180 may be defined by one or more deposition apertures in aflexible aperture mask web 10. Alternatively, one or more of the layersof the thin film transistor may be defined by a number of differentpatterns in aperture mask web 10. In that case, stitching techniques, asmentioned above, may be used.

By forming deposition apertures 14 in aperture mask webs 10 to besufficiently small, one or more features of thin film transistor 180 canbe made less than approximately 1000 microns, less than approximately 50microns, less than 20 microns, less than 10 microns, or even less than 5microns. Moreover, by forming a gap in aperture mask webs 10 to besufficiently small, other features such as the distance between sourceelectrode 185 and drain electrode 186 can be made less thanapproximately 1000 microns, less than approximately 50 microns, lessthan 20 microns or even less than 10 microns. In that case, a singlemask pattern may be used to deposit second conductive layer 184, witheach of the two electrodes 185, 186 being defined by depositionapertures separated by a sufficiently small gap, such as a gap less thanapproximately 1000 microns, less than approximately 50 microns, lessthan approximately 20 microns or a gap less than approximately 10microns. In this manner, the size of thin film transistor 180 can bereduced, enabling fabrication of smaller, higher density circuitry whileimproving the performance of thin film transistor 180. Additionally, acircuit comprising two or more transistors, like that illustrated inFIG. 17 can be formed by an aperture mask web having two depositionapertures of a pattern separated by a large distance, as illustrated inFIGS. 3 and 4.

FIG. 18 illustrates another embodiment of a thin film transistor 190. Inparticular, thin film transistor 190 includes a first depositedconductive layer 192 formed over deposition substrate 191. A depositeddielectric layer 193 is formed over first conductive layer 192. Adeposited active layer 194, such as a deposited semiconductor layer, ora deposited organic semiconductor layer is formed over depositeddielectric layer 193. A second deposited conductive layer 195 definingsource electrode 196 and drain electrode 197 is formed over depositedactive layer 194.

Again, by forming deposition apertures 14 in aperture mask webs 10 to besufficiently small, one or more features of thin film transistor 190 canhave widths on the order of those discussed herein. Also, by forming agap between apertures in aperture mask webs 10 to be sufficiently small,the distance between source electrode 196 and drain electrode 197 can beon the order of the gap sizes discussed herein. In that case, a singlemask pattern may be used to deposit second conductive layer 195, witheach of the two electrodes 196, 197 being defined by depositionapertures separated by a sufficiently small gap. In this manner, thesize of thin film transistor 190 can be reduced, and the performance ofthin film transistor 190 improved.

Thin film transistors implementing organic semiconductors generally takethe form of FIG. 17 because organic semiconductors cannot be etched orlithographically patterned without damaging or degrading the performanceof the organic semiconductor material. For instance, morphologicalchanges can occur in an organic semiconductor layer upon exposure toprocessing solvents. For this reason, fabrication techniques in whichthe organic semiconductor is deposited as a top layer may be used. Theconfiguration of FIG. 18 is advantageous because top contacts to theelectrodes provide a low-resistance interface.

By forming at least the top two layers of the thin film transistor usingaperture mask deposition techniques, the invention facilitates theconfiguration of FIG. 18, even if active layer 194 is an organicsemiconductor layer. The configuration of FIG. 18 can promote growth ofthe organic semiconductor layer by allowing the organic semiconductorlayer to be deposited over the relatively flat surface of dielectriclayer 193, as opposed to being deposited over the non-continuous secondconductive layer 184 as illustrated in FIG. 17. For example, if theorganic semiconductor material is deposited over a non-flat surface,growth can be inhibited. Thus, to avoid inhibited organic semiconductorgrowth, the configuration of FIG. 18 may be desirable. In someembodiments, all of the layers may be deposited as described above.Also, the configuration of FIG. 18 is advantageous because depositingappropriate source and drain electrodes on the organic semiconductorprovides low-resistance interfaces. Additionally, circuits having two ormore transistors separated by a large distance can also be created, forexample, using aperture mask webs like those illustrated in FIGS. 3 and4.

A number of embodiments of the invention have been described. Forexample, a number of different structural components and differentaperture mask deposition techniques have been described for realizing anin-line deposition system. The deposition techniques can be used tocreate various circuits solely using deposition, avoiding any chemicaletching processes or photolithography, which is particularly useful whenorganic semiconductors are involved. Moreover, the system can beautomated to reduce human error and increase throughput. Nevertheless,it is understood that various modifications can be made withoutdeparting from the spirit and scope of the invention. For example,although some aspects of the invention have been described for use in athermal vapor deposition process, the techniques and structuralapparatuses described herein could be used with any deposition processincluding sputtering, thermal evaporation, electron beam evaporation andpulsed laser deposition. Thus, these other embodiments are within thescope of the following claims.

1. A method comprising: positioning first and second webs of film inproximity to each other, wherein the second web of film defines adeposition mask pattern; depositing material on the first web of filmthrough the deposition mask pattern defined by the second web of film tocreate at least a portion of an integrated circuit; and stretching atleast one web of film to align the deposition mask pattern relative tothe first web of film prior to disposition.
 2. The method of claim 1,comprising: stretching the second web of film in a down-web direction toalign the deposition mask pattern relative to the first web of filmprior to deposition.
 3. The method of claim 1, comprising: stretchingthe second web of film in a cross-web direction to align the depositionmask pattern relative to the first web of film prior to deposition. 4.The method of claim 1, comprising: stretching the first web of film in adown-web direction to align the deposition mask pattern relative to thefirst web of film prior to deposition.
 5. The method of claim 1,comprising: stretching the first web of film in a cross-web direction toalign the deposition mask pattern relative to the first web of filmprior to deposition.
 6. A method of creating integrated circuitscomprising: passing a first elongated web of flexible film through anumber of vacuum deposition chambers; and sequentially depositingpatterned layers of material on the web of flexible film in each vacuumdeposition chamber.
 7. The method of claim 6, wherein deposition of alayer corresponding to a second layer in a second vacuum depositionchamber occurs at substantially the same time as deposition of a layercorresponding to a first layer in a first vacuum deposition chamber. 8.The method of claim 6, further comprising separating the first elongatedweb of flexible film into a number of integrated circuits.
 9. The methodof claim 8, wherein each circuit comprises a radio frequencyidentification (RFID) circuit.